This invention relates generally to mine roof tool bit inserts and particularly to an insert having an improved arrangement of cutting edges.
Mine roofs require stabilization to ensure that they will support the load of the roof and effective stabilization can be achieved by means of inserting elongated roof bolts into the roof. The use of such roof bolts require the forming of elongated holes drilled directly into the roof and it is important that the bit inserts which form these holes have effective cutting edges but also have a long wear life.
Typically the bit inserts are made from a flat elongated body formed from identical halves rotatable about a central axis, each half having top and end cutting edges, the top cutting edge being inclined to the axis of rotation and the end cutting edge being generally parallel to the axis of rotation. The top cutting edge and the side cutting edge are usually provided with a relief angle between the cutting, or leading, edge and the trailing edge.
Various cutting edge arrangements have been developed by modifying the geometry of the bit insert to improve the wear resistance. For example, U.S. Pat. No. 4,787,464 discloses a bit insert having a leading (side) face inclined at small angle relative to the axis of rotation and a frontal (top) face having a variable relief angle. U.S. Pat. No. 4,527,638 on the other hand provides a bit insert having a top face with a constant relief angle, but having a radiused corner between the top cutting edge and the end cutting edge. In another reference, U.S. Pat. No. 4,696,352, the bit insert is coated with one or more adherent layers of a refractory coating material to increase wear resistance.
While the above bit inserts may be effective for their intended purpose of increasing wear resistance such improvement is achieved by providing a relatively complex geometry or an expensive coating.
The present improved bit insert provides greater wear resistance without these disadvantages.